Roofing granule mixtures for algae-resistant roofing shingles

ABSTRACT

The present disclosure relates generally to a roofing granule mixture, the mixture comprising a first class of roofing granules consisting of non-algae-resistant roofing granules, and a second class of roofing granules consisting of algae-resistant roofing granules having a d50 particle size of at most 0.9 mm.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority of U.S. Provisional Patent Application No. 63/294,733, filed Dec. 29, 2021, which is hereby incorporated herein by reference in its entirety.

BACKGROUND OF THE DISCLOSURE 1. Field of the Disclosure

The present disclosure relates generally to roofing products. The present disclosure relates more particularly to mixtures of roofing granules, comprising algae-resistant granules, algae-resistant roofing shingles, and methods of making the same.

2. Technical Background

Roofing granules are generally used on the top surfaces of asphalt shingles and roofing membranes to provide a variety of functions, such as protecting the asphalt from harmful ultraviolet radiation and adding aesthetic value to the roof via coloration of the granules. Roofing granules are typically based on crushed and screened mineral material, which can be coated subsequently with one or more coloring pigments, such as suitable metal oxides, disposed in a binder.

Depending on location and climate, roofing materials can experience very challenging environmental conditions. Over time, particularly in warmer, humid climates, conventional roofing shingles can develop dark blotches or streaks that are aesthetically unpleasant. These blotches and streaks are the results of algae growth on the surface of the roofing product. This is especially true in climates with high humidity and high temperatures, such as in Hawaii and Florida. This can significantly decrease the effective service life of such roofs

One approach to combat algae growth is to include algae-resistant granules on the exposed surface of the roofing material. Such granules may, for example, have a layer including an algaecide. Both copper and zinc compounds (e.g., oxides) are typically used as algaecides, as they leach algaecidal copper and zinc ions over time with exposure to rain. Although algae-resistant granules are effective at combating algae growth, it can be difficult to maintain the necessary performance over the lifetime of the typical 10 year warranty, especially in hot and humid environments like Florida and Hawaii. One potential solution to increase the longevity of the algae-resistant roofing products is to include more algae-resistant granules on the roofing products, or add more algaecide to the granules. However, these options would have a significant cost impact on current roofing products.

Accordingly, there is a need in the art to develop cost-effective methods to produce algae-resistant roofing products with improved longevity.

SUMMARY OF THE DISCLOSURE

In one aspect, the present disclosure provides a roofing granule mixture, the mixture consisting of:

-   -   a first class of roofing granules consisting of         non-algae-resistant roofing granules; and     -   a second class of roofing granules consisting of algae-resistant         roofing granules having a d50 particle size of at most 0.9 mm.

Another aspect of the present disclosure provides a method of producing a mixture of roofing granules as described herein, the method comprising:

-   -   providing a plurality of base particles;     -   splitting the plurality of base particles into a first batch and         a second batch,         -   wherein the second batch of base particles have a d50             particle size of at most 0.9 mm;     -   applying a first top coat to the first batch to form a first         class of roofing granules, wherein the first top coat comprises         at least one colorant;     -   applying a second top coat to the second batch to form a second         class of roofing granules, wherein the second top coat comprises         at least one algaecide and at least one colorant; and     -   blending the first class of roofing granules and the second         class of roofing granules, wherein the second class of roofing         granules are present in an amount in the range of 1-30 wt % of         the total mixture.

Another aspect of the present disclosure provides an algae-resistant roofing shingle comprising a shingle substrate; and adhered to a top surface of the shingle substrate, the roofing granule mixture as described herein.

Another aspect of the present disclosure provides a method for producing an algae-resistant roofing shingle comprising providing a shingle substrate; and adhering to a top surface of the shingle substrate the roofing granule mixture as described herein.

BRIEF DESCRIPTION OF FIGURES

FIG. 1 is a graph of the particle size distribution of conventional algae-resistant roofing granules and of the particle size distribution of the second class of roofing granules according to one embodiment of the present disclosure.

FIG. 2 is a picture of a roofing product covered with a mixture of roofing granules comprising non-algae-resistant roofing granules and conventional algae-resistant copper roofing granules and FIG. 3 is a picture of a roofing product covered with a mixture of roofing granules comprising a first class of roofing granules consisting of non-algae-resistant granules and a second class of roofing granules consisting of algae-resistant granules according to one embodiment of the present disclosure.

FIG. 4 is a set of pictures comparing algae resistance tests on samples with conventional algae-resistant granules with algae-resistant granules of the disclosure.

DETAILED DESCRIPTION

The present inventors have noted that current algae-resistant roofing products, e.g., algae-resistant roofing shingles, do not have the longevity to provided effective algae resistance over the 10-year warranty lifetime of the product. The present inventors also note some solutions, such as the inclusion of a higher loading of algae-resistant granules to shingles or the inclusion of a higher loading of algaecides to granules, can greatly increase the cost of roofing products. Here, the inventors have determined that by decreasing the size of algae-resistant granules, the effective surface area of the algae-resistant granules presented to the environment can be increased without increasing the weight percent of algae-resistant roofing granules applied to the shingle. Accordingly, the present inventors use algae-resistant granules having a d50 particle size of at most 0.9 mm (e.g., at most 0.6 mm) in admixture with conventional roofing granules. As described herein, this can provide a number of advantages, including, in various embodiments, improved algaecidal performance, improved color performance, and better use of feed materials. For example, algaecidal granules often have a dark color; relatively smaller granules can provide less of a perceived color darkening to the shingle for an equivalent algaecidal activity. Smaller granules can distribute more evenly on a surface of a shingle, so that there is less chance of areas that are not effectively protected by algaecide.

In one aspect, the present disclosure provides a roofing granule mixture that consists of a first class of roofing granules consisting of non-algae-resistant roofing granules and a second class of roofing granules consisting of algae-resistant roofing granules having a d50 particle size of at most 0.9 mm. As used herein, the “first class” of roofing granules includes all of the non-algaecidal roofing granules of the mixture, and the “second class” of roofing granules includes all of the algaecidal roofing granules of the mixture.

As used herein, when referring to a particle size distribution, “d” followed by a number refers to the percentile of the distribution that is less than a particular size. For example, d50 of 1 mm means that 50% of the particles have a particle size of 1 mm or smaller. d50, d10 and d90 particle sizes can be measured by conventional laser diffraction techniques, e.g., by a Mastersizer 3000 particle size analyzer.

In some embodiments of the present disclosure, the first class of roofing granules has a relatively large size, as is conventionally used in granule-coated roofing products. For example, in various embodiments, the first class of roofing granules has a d50 particle size in the range of 0.7 mm to 5 mm, e.g., in the range of 0.7 to 3 mm, or 0.7 to 2 mm. In particular embodiments, the first class of roofing granules has a d50 particle size in the range of 1 mm to 5 mm, e.g., in the range of 1 mm to 3 mm, or 1 mm to 2 mm. In other particular embodiments, the first class of roofing granules has a d50 particle size in the range of 1.5 mm to 5 mm, e.g., in the range of 1.5 mm to 3 mm, or 1.5 mm to 2.5 mm.

The first class of roofing granules are typically the majority of the roofing granules in the mixture. For example, in some embodiments of the present disclosure, the first class of roofing granules is present in the roofing granule mixture in an amount in the range of 70-99 wt % of the total mixture, e.g., in an amount in the range of 70-95 wt %, or 70-90 wt %, or 70-85 wt %, or 70-80 wt %, or 75-95 wt %, or 75-90 wt %, or 75-85 wt %. For example, in particular embodiments, the first class of roofing granules are present in the roofing granule mixture in an amount in the range of 80-99 wt % of the total mixture, e.g., in an amount in the range of 80-95 wt %, or 80-90 wt %, or 85-95 wt % of the total mixture.

The first class of roofing granules consists of non-algae-resistant roofing granules. The non-algae-resistant roofing granules are not particularly limited and can be selected from any non-algae-resistant roofing granule as would be known to the person of ordinary skill in the art. For example, the first class of roofing granules may be selected from conventional roofing granules, solar-reflective roofing granules, water-resistant roofing granules, or a combination thereof. The first class of roofing granules can be provided in a variety of colors or mixtures of colors as is conventional in the art.

The person of ordinary skill in the art will select a desired size distribution and desired relative amount of the first class of roofing granules to provide a desired coverage and aesthetic effect on the shingle.

As noted above, the second class of roofing granules has a relatively small median particle size, i.e., a d50 of at most 0.9. In some embodiments, the second class of roofing granules has a d50 particle size of at most 0.8 mm, e.g., of at most 0.7 mm. For example, in some embodiments, the second class of roofing granules has a d50 particle size of at most 0.6 mm, e.g., at most 0.5 mm.

In various embodiments, the second class of roofing granules does not have a high proportion of very small particles. For example, in some embodiments, the second class of roofing granules has a d10 particle size of at least 0.1 mm, e.g., at least 0.2 mm.

Similarly, in various embodiments, the second class of roofing granules does not have a high proportion of very large particles. For example, in some embodiments, the second class of roofing granules has a d90 particle size of at most 1.5 mm, e.g., at most 1.0 mm, or at most 0.8 mm.

In various embodiments, the second class of roofing granules is substantially smaller than the first class of roofing granules. For example, in some embodiments, the second class of roofing granules has a d50 particle size that is no more than 70%, e.g., no more than 60%, of the d50 particle size of the first class of roofing granules. In some embodiments, the second class of roofing granules has a d50 particle size that is no more than 50%, e.g., no more than 40%, of the d50 particle size of the first class of roofing granules.

FIG. 1 illustrates the size distribution differences between conventional-size algae-resistant roofing granules and the second class of roofing granules of one embodiment of the present disclosure. The x-axis lists various US mesh sizes; the fraction of material listed for a particular mesh size is retained by that mesh and passed by the immediately larger mesh. The conventional algae-resistant roofing granules have a broader particle size distribution than that of the second class of roofing granules and have a larger average size than the second class of roofing granules. Specifically, the particle size distribution of conventional algae-resistant roofing granules ranges from a U.S. mesh size of #40 to #8, with greater than 70% of the granules being in the range of U.S. mesh size #20 to #16. In contrast, the second class of roofing granules of one embodiment of the disclosure as described herein has a particle size distribution in the range of U.S. mesh size #40 to #20, with greater than 80% having a size of U.S. mesh size of #30.

The algae-resistant granules of the second class are typically present in a relatively minor amount. In some embodiments of the present disclosure, the second class of roofing granules are present in an amount in the range of 1-30 wt % of the total mixture, e.g., in an amount in the range of 1-25 wt %, or 1-20 wt %, or 1-15 wt %, or 1-10 wt %, or 3-30 wt %, or 3-25 wt %, or 3-20 wt %, or 3-15 wt %, or 3-10 wt %, or 5-30 wt %, or 5-25 wt %, or 5-20 wt %, or 5-15 wt % of the total mixture. In some embodiments, the second class of roofing granules are present in an amount in the range of 10-30 wt % of the total mixture, e.g., in an amount in the range of 10-25 wt %, or 10-20 wt %, or 15-30 wt %, or 15-25 wt %, or 20-30 wt % of the total mixture.

The second class of roofing granules consists of algae-resistant roofing granules. The algae-resistant roofing granules are not particularly limited and can be selected from any algae-resistant roofing granule as known to the person of ordinary skill in the art. For example, in certain embodiments of the disclosure as described herein, the second class of roofing granules comprise an organic algaecide, an inorganic algaecide, or a combination thereof.

In particular embodiments, each of the second class of roofing granules comprise an organic algaecide. The organic algaecide is not particularly limited and can be selected from any organic algaecide as known in the art. For example, the organic algaecide is independently selected from zinc pyrithione or 4,5-dichloro-2-n-octyl-4-isothiazoline-3-one (DCOIT).

In particular embodiments, each of the second class of roofing granules comprise an inorganic algaecide. For example, the inorganic algaecide of the second class of roofing granules is independently selected from the group consisting of copper species (e.g., copper oxide), zinc species (e.g., zinc oxide), silver species, and anatase titanium oxides. In particular embodiments, the inorganic algaecide of the second class of roofing granules is a copper species (e.g., copper oxide), or a zinc species (e.g., zinc oxide). For example, in certain embodiments of the present disclosure as described herein, the inorganic algaecide of the second class of roofing granules is a copper species (e.g., copper oxide). Mixtures of different inorganic algaecides can be used, e.g., together in a single granule, or in different granules of the second class of roofing granules.

As will be appreciated by the person of ordinary skill in the art, the algae-resistant roofing granules may include a base particle on which an algaecide-containing layer is disposed. In certain embodiments, the second class of roofing granules and as otherwise described herein comprises a base particle at least partially surrounded by the algaecide-containing layer. In particular embodiments, the base particle is entirely surrounded by the algaecide-containing layer. As described in more detail below, base particles can be coated with the algaecide-containing layer using methods analogous to those used in making conventional roofing granules.

In other embodiments of the algae-resistant roofing granules as otherwise described herein, no base particle is used. In such cases, a composition itself comprising an algaecide can provide a body of the granule.

The algaecide according to the present disclosure may be provided in a range of weight loadings in order to tune roofing granule properties. It may be desired to maximize the algaecide weight loading, or achieve a particular weight loading. The amount of algaecide disposed within the roofing granule may be tuned as required to effect algaecidal activity over long periods of time. In certain embodiments as otherwise described herein, the algaecide is present in the second class of roofing granules in the range of 1 wt % to 50 wt %, e.g., 5 wt % to 50 wt %, or 10 wt % to 50 wt %, or 15 wt % to 50 wt % of the granule mass. In certain embodiments, the algaecide is present in the second class of roofing granule in the range of 1 wt % to 25 wt %, e.g., 5 wt % to 25 wt %, or 10 wt % to 25 wt % of the granule mass. In certain embodiments, the algaecide is present in the second class of roofing granule in the range of 1 wt % to 15 wt %, e.g., 5 wt % to 15 wt %, or 1 wt % to 10 wt % of the granule mass.

In certain embodiments as otherwise described herein, the algaecide is disposed at an outer surface of the roofing granule. However, in other embodiments, a top coat can be formed at the outer surface of the granule, i.e., with the algaecide disposed beneath the top coat. Here, while there is a substantial layer of algaecide-containing material just under the surface, there is a top coat coated around a composition comprising the algaecide. The present inventors have noted that a top coat can perform a number of useful functions. Critically, a top coat can be used to modify the rate of leaching. It can also be used to provide color to the granule, or provide an additional source of the algaecide.

For example, the top coat may be used to alter (e.g., retard) the leaching profile of the algaecide from the algae-resistant roofing granule. Provision of a top coat that comprises substantially no algaecide will serve to slow the leaching of the algaecide from the algae-resistant roofing granule, advantageously leading to algae-resistance for a longer period of time. The person of ordinary skill in the art can tune the leaching rate, e.g., by providing different thicknesses and/or porosities of the top coat. For example, in certain embodiments, the top coat is in the range of 1-300 microns in thickness, e.g., 1-100 microns.

A major drawback of conventional algae-resistant roofing granules is the use of copper oxide, which is naturally a dark black solid. As such, high copper oxide loadings often result in very dark granules; while this may be desirable for some color schemes, it means that other desirable color schemes cannot be utilized. The present disclosure provides for the use of much smaller copper granules, which can provide less of a darkening to an overall combination of granules when compared to conventional copper granules. Advantageously, this allows for an expanded color palette and incorporation of smaller algae-resistant roofing granules into an expanded range of roofing products.

Another aspect of the disclosure provides a method of producing a mixture of roofing granules as described herein. The method comprises, providing a plurality of base particles; splitting the plurality of base particles into a first batch and a second batch, wherein the second batch of bae particles have a d50 particle size of at most 0.9 mm and that is smaller than the d50 particle size of the first batch; applying a first top coat to the first batch to form a first class of roofing granules, wherein the first top coat comprises at least one colorant; applying a second top coat to the second batch to form a second class of roofing granules, wherein the second top coat comprises at least one algaecide and at least one colorant; and blending the first class of roofing granules and the second class of roofing granules, wherein the second class of roofing granules are present in an amount in the range of 1-30 wt % of the total mixture. For example, the first top coat and second top coat can be substantially the same but for the use of the algaecide (e.g., copper compound, zinc compound, titanium oxide, organic algaecide) in the second top coat. The first class and second class of roofing granules can as otherwise be described herein, e.g., with respect to particle size and relative amounts. The second batch can have, for example, a d50 particle size that is no more than 70%, e.g., no more than 60%, of the d50 particle size of the first batch. In various embodiments, the second batch has a d50 particle size that is no more than 50%, e.g., no more than 40%, of the d50 particle size of the first batch. Advantageously, if the same colorant is used on both the first and second batches of base particles, they can have very similar colors and provides enhanced shingle aesthetics.

Conventional materials can be used to make the roofing granules described herein. The first class of roofing granules, the second class of roofing granules may include a base particle. The person of ordinary skill in the art will appreciate that a variety of materials can be used as base particles for the non-algae-resistant and algae-resistant roofing granules. In certain embodiments, the base particle is an inert mineral particle. Examples of the suitable base particles include rocks, stone dust, crushed slate, slate granules, shale granules, granule chips, mica granules and metal flakes. But others can be used.

In other embodiments, the base particle of the non-algae-resistant and algae-resistant roofing granule is a synthetic particle. A variety of methods can be used to make particles suitable for use as base particles, e.g., from clays and other preceramic materials. Examples of such materials include those described, for example, in U.S. Pat. No. 7,811,630, U.S. Patent Applications Publications nos. 2010/0151199, 2010/0203336, and 2018/0186994, each of which is hereby incorporated herein by reference in its entirety. For example, the base particles can be formed by forming a preceramic material in desired shapes, then firing that formed material to provide base particles. The preceramic material can be, for example, a mixture of particulate material with a suitable binder, such as the binders otherwise described herein. A wide variety of particulate materials can be used, e.g., stone dust, granule fines, can be used. In other embodiments, a clay such as bauxite or kaolin can be used as the preceramic material. Extrusion, casting or like process can in some embodiments be used to provide base particles having the sizes and aspect ratios desired. Examples of processes for providing base particles having a predetermined desired shape are given by U.S. Pat. No. 7,811,630, which is incorporated herein by reference in its entirety.

Advantageously, a binder can be provided as part of the non-algae-resistant and algae-resistant granule to bind together individual stone dust. A wide variety of binders can be used. The binder precursors can also include an alkali aluminosilicate clay. As the person of ordinary skill in the art will appreciate, alkali silicate and alkali aluminosilicate clay are often used together as binder precursors to make coatings of conventional roofing granules. In certain embodiments, the alkali aluminosilicate clay is kaolin or bauxite. In certain embodiments of the non-algae-resistant and algae-resistant roofing granules as otherwise described herein, a fireable mixture includes as a binder precursor an alkali silicate such as sodium silicate. The alkali/sodium silicate of the binder is a component separate from any kaolin or other alkali aluminosilicate clay present, and thus the alkali/sodium silicate component is not considered to include any alkali/sodium silicate present in the kaolin or other alkali aluminosilicate clay.

The person of ordinary skill in the art will, based on the disclosure herein, select an amount of a sodium silicate, in combination with the other component(s), that provides the desired properties to the non-algae-resistant and algae-resistant roofing granules. For example, in certain embodiments of the non-algae-resistant and algae-resistant roofing granules as otherwise described herein, the sodium silicate is present in the fireable composition in an amount in the range of 5-60 wt % (i.e., exclusive of water or any solvent used to moisten the mixture for formability). In various embodiments of the roofing granules as otherwise described herein, the sodium silicate is present in the binder in an amount in the range of 5-45 wt %, or 5-30 wt %, or 5-20 wt %, or 10-60 wt %, or 10-45 wt %, or 10-30 wt %, or 10-20 wt %, or 20-60 wt %, or 20-45 wt %.

In certain embodiments of the non-algae-resistant and algae-resistant roofing granules as otherwise described herein, the aluminosilicate clay of the fired mixture is a kaolin clay. As the person of ordinary skill in the art will appreciate, a “kaolin clay” or “kaolin” is a material comprising kaolinite, quartz and feldspar. The person of ordinary skill in the art will appreciate that a variety of types or grades of kaolin can be used. The kaolin used in the roofing granules described herein can be (or can include), for example, a kaolin crude material, including kaolin particles, oversize material, and ferruginous and/or titaniferous and/or other impurities, having particles ranging in size from submicron to greater than 20 micrometers in size. Alternatively, in certain desirable embodiments, a refined grade of kaolin clay can be employed, such as, for example, a grade of kaolin clay including mechanically delaminated kaolin particles. Further, grades of kaolin such as those coarse grades used to extend and fill paper pulp and those refined grades used to coat paper can be employed in the roofing granules as described herein. Examples of kaolins suitable for use in the non-algae-resistant and algae-resistant roofing granules as described herein include, for example, EPK Kaolin (Edgar Materials), for example in jet-milled form; Kaobrite 90 (Thiele Kaolin); and SA-1 Kaolin (Active Minerals). Kaolins can be subjected to any of a number of conventional processes to beneficiate them, e.g., blunging, degritting, classifying, magnetically separating, flocculating, filtrating, redispersing, spray drying, pulverizing and firing.

In certain embodiments of the non-algae-resistant and algae-resistant roofing granules as otherwise described herein, a different alkali aluminosilicate clay can be used in combination with or instead of the kaolin. For example, in certain embodiments of the roofing granules as otherwise described herein, the aluminosilicate clay is (or includes) bauxite. In certain embodiments of the non-algae-resistant and algae-resistant roofing granules as otherwise described herein, the aluminosilicate clay is (or includes) chamotte. In certain embodiments of the non-algae-resistant and algae-resistant roofing granules as otherwise described herein, the aluminosilicate clay is (or includes) a white clay such as ball clay or montmorillonite. In certain embodiments of the roofing granules as otherwise described herein, the aluminosilicate clay is (or includes) a white clay such as ball clay or montmorillonite. However, in certain desirable embodiments, at least 50 wt %, e.g., at least 70 wt %, at least 80 wt %, at least 90 wt %, or even at least 95 wt % of the aluminosilicate clay is kaolin.

The person of ordinary skill in the art will, on the basis of the description provided herein, select alkali aluminosilicate clay(s) that provide a high degree of whiteness, and thus a high degree of solar reflectivity. Two important impurities present in alkali aluminosilicate clays such as kaolin are iron and titanium. Iron can create highly-colored impurities, especially upon firing and especially when present in combination with titanium. Accordingly, in certain desirable embodiments of the non-algae-resistant and algae-resistant roofing granules as otherwise described herein, the alkali aluminosilicate clay of the binder has no more than 1 wt % iron, e.g. no more than 0.7 wt % or no more than 0.5 wt % iron, as measured by inductively-coupled plasma mass spectrometry (ICP-MS) and reported as Fe₂O₃. Similarly, in certain desirable embodiments of the roofing granules as otherwise described herein, the alkali aluminosilicate clay of the binder has no more than 1 wt % titanium, e.g., no more than 0.7 wt % no more than 0.5 wt % titanium, measured by ICP-MS and reported as TiO₂. The person of ordinary skill in the art can select suitable clays having low amounts of iron and titanium.

In certain embodiments of the non-algae-resistant and algae-resistant roofing granules as otherwise described herein, the alkali aluminosilicate clay is present in the binder in an amount in a range up to 80 wt % (i.e., exclusive of water or any solvent used to moisten the mixture for formability). For example, in various embodiments of the roofing granules as otherwise described herein, the alkali aluminosilicate clay is present in the fireable mixture in an amount up to 65 wt %, or up to 50 wt %. In certain embodiments, the aluminosilicate clay is present in the fireable mixture in an amount in the range of 5-80 wt %, or 10-80 wt %, or 20-80 wt %, or 5-65 wt %, or 10-65 wt %, or 20-65 wt %, or 5-50 wt %, or 10-50 wt %, or 20-50 wt %. The person of ordinary skill in the art will, based on the disclosure herein, select an amount of alkali aluminosilicate clay, e.g., in combination with other components, that provides the desired properties to the algae-resistant roofing granules.

In addition to the alkali aluminosilicate, the aluminosilicate fireable mixture may include a variety of components as known in the art, including other binders or precursors therefor, and colorants such as pigments and dyes, which can desirably be reflective of solar radiation, especially in the near-infrared range. Suitable colorants are described below with respect to the optional top coat.

Splitting the plurality of base particles into a first batch and a second batch can be accomplished based on the relative sizes of the base particles. A number of size classification methods are familiar to the person of ordinary skill in the art. Sieving can advantageously be used, with base particles retained by a sieve being in the first batch, and base particles passing through the sieve being in the second bat. For example, in certain embodiments, the base particles are split using a sieve with a mesh size of at least US #16, or at least US #20, or US #25, or US #30.

A top coat can conveniently be disposed on an outer surface of a base particle, such that it is fired together with the base particle to cure it. Such a material can be based on binders similar to those of the aluminosilicate fireable mixture. For example, in certain embodiments, the coating used to provide the top coat may include an alkali silicate (e.g., sodium silicate) optionally together with an aluminosilicate clay (e.g., kaolin clay). But in other embodiments, e.g., when an organic binder is used, the top coat can be applied to the fired granules.

The top coat may further comprise colorants, pigments and/or minerals as otherwise described herein. Advantageously, the top coat can provide a desired color to the roofing granule through the use of pigments or other colorants; when provided in a suitably thin layer, the topcoat can nonetheless allow algaecidal ions to leach therethrough. For example, a top coat can be used to provide color to the granule, in cases where there is no colorant in the non-algae-resistant granules or algae-resistant granules, or to work with color that is visible in either type of granule.

In certain embodiments, the top coat may be coated onto the base particle by fluidized bed coating. Similarly, for algae-resistant roofing granules, the algaecide may be applied to the base particle by fluidized bed coating. Fluidized bed coating is described in U.S. Patent Application Publication no 2006/0251807 A1, which is hereby incorporated herein by reference in its entirety. This type of coating device can be employed to provide the layers of the top coat and/or the algaecide as precise and uniform coatings, e.g., on a base particle. Wurster-type fluidized bed spray devices are available from a number of vendors, including Glatt Air Techniques, Inc., Ramsey, N.J. 07446; Chungjin Tech. Co. Ltd., South Korea; Fluid Air Inc., Aurora, III. 60504, and Niro Inc., Columbia, Md. 21045. Modified Wurster-type devices and processes, such as, the Wurster-type coating device disclosed in U.S. Patent Publication 2005/0069707, incorporated herein by reference, for improving the coating of asymmetric particles, can also be employed. In addition, lining the interior surface of the coating device with abrasion-resistant materials can be employed to extend the service life of the coater.

Other types of batch process particle fluidized bed spray coating techniques and devices can be used. For example, the particles (e.g., base particles) can be suspended in a fluidized bed, and the coating material (e.g. the top coat and/or algaecide) can be applied tangentially to the flow of the fluidized bed, as by use of a rotary device to impart motion to the coating material droplets.

In the alternative, other types of particle fluidized bed spray coating can be employed. For example, the particles can be suspended as a fluidized bed, and coated by spray application of a coating material from above the fluidized bed. In another alternative, the particles can be suspended in a fluidized bed, and coated by spray application of a coating material from below the fluidized bed, such as is described in detail above. In either case, the coating material can be applied in either a batch process or a continuous process. In coating devices used in continuous processes, uncoated particles enter the fluidized bed and can travel through several zones, such as a preheating zone, a spray application zone, and a drying zone, before the coated particles exit the device. Further, the particles can travel through multiple zones in which different coating layers are applied as the particles travel through the corresponding coating zones.

Notably, the parameters of the fluidized bed coating process will determine the nature, extent, and thickness of the coating formed. For example, the properties of a material provided in a Wurster-type fluidized bed spray device depends upon a number of parameters including the residence time of the particles in the device, the height of the Wurster tube, the particle shape, the particle size distribution, the temperature of the suspending airflow, the temperature of the fluidized bed of particles, the pressure of the suspending airflow, the pressure of the atomizing gas, the composition of the coating material, the size of the droplets of coating material, the size of the droplets of coating material relative to the size of the particles to be coated, the spreadability of the droplets of coating material on the surface of the particles to be coated, the loading of the device with the mineral particles or batch size, the viscosity of the coating material, the physical dimensions of the device, and the spray rate.

In other such embodiments, the top coat and/or algaecide is coated onto a base particle by a coating method other than fluidized bed coating, for example, pan coating, granulation, magnetically assisted impaction coating or spinning disc coating. For example, magnetically assisted impaction coating (“MAIC”) available from Aveka Corp., Woodbury, Minn., can be used to coat granules with solid particles such as titanium dioxide. Other techniques for coating dry particles with dry materials can also be adapted for use in the present process, such as the use of a Mechanofusion device, available from Hosokawa Micron Corp., Osaka, JP; a Theta Composer device, available from Tokuj Corp., Hiratsuka, JP, and a Hybridizer device, available from Nara Machinery, Tokyo, JP. In the spinning disc method the granules and droplets of the liquid coating material are simultaneously released from the edge of a spinning disk, such as disclosed, for example, in U.S. Pat. No. 4,675,140.

The top coat may further comprise pigments and/or minerals as otherwise described herein. Advantageously, the top coat can provide a desired color to the roofing granule through the use of pigments or other colorants; when provided in a suitably thin layer, the top coat can nonetheless allow an algaecide to leach therethrough in the case of algae-resistant roofing granules. For example, a top coat can be used to provide color to the granule, in cases where there is no colorant in the non-algae-resistant or algae-resistant roofing granules, or to work with color that is visible in the non-algae-resistant or algae-resistant granules.

As the person of ordinary skill will appreciate, a variety of materials can be used as pigments in the roofing granules for use herein (e.g., in a top coat or fireable mixture). Titanium dioxides such as rutile titanium dioxide and anatase titanium dioxide, metal pigments, titanates, and mirrorized silica pigments can be used as solar-reflective pigments. Other pigments that can be adapted for use include zinc oxide, lithopone, zinc sulfide, white lead, and organic and inorganic opacifiers such as glass spheres. Of course, materials can be used in combination to provide desirable solar reflectivities and desirable mechanical properties to the roofing granules.

Examples of mirrorized silica pigments that can be used in the roofing granules (e.g., in a top coat or fireable mixture) for use herein include pigments such as Chrom Brite™ CB4500, available from Bead Brite, 400 Oser Ave, Suite 600, Hauppauge, N.Y. 11788.

An example of a rutile titanium dioxide that can be employed in the roofing granules for use herein includes R-101, available from Chemours.

Examples of metal pigments that can be employed in the roofing granules for use herein include aluminum flake pigment, copper flake pigments, copper alloy flake pigments, and the like. Metal pigments are available, for example, from ECKART America Corporation, Painesville, Ohio 44077. Suitable aluminum flake pigments include water-dispersible lamellar aluminum powders such as Eckart RO-100, RO-200, RO-300, RO-400, RO-500 and RO-600, non-leafing silica coated aluminum flake powders such as Eckart STANDART PCR 212, PCR 214, PCR 501, PCR 801, and PCR 901, and STANDART Resist 211, STANDART Resist 212, STANDART Resist 214, STANDART Resist 501 and STANDART Resist 80; silica-coated oxidation-resistant gold bronze pigments based on copper or copper-zinc alloys such as Eckart DOROLAN 08/0 Pale Gold, DOROLAN 08/0 Rich Gold and DOROLAN 10/0 Copper.

Examples of titanates that can be employed in the roofing granules for use herein include titanate pigments such as colored rutile, priderite, and pseudobrookite structured pigments, including titanate pigments comprising a solid solution of a dopant phase in a rutile lattice such as nickel titanium yellow, chromium titanium buff, and manganese titanium brown pigments, priderite pigments such as barium nickel titanium pigment; and pseudobrookite pigments such as iron titanium brown, and iron aluminum brown. The preparation and properties of titanate pigments are discussed in Hugh M. Smith, High Performance Pigments, Wiley-VCH, pp. 53-74 (2002).

Examples of near IR-reflective pigments available from the Shepherd Color Company, Cincinnati, Ohio, include Arctic Black 10C909 (chromium green-black), Black 411 (chromium iron oxide), Brown 12 (zinc iron chromite), Brown 8 (iron titanium brown spinel), and Yellow 193 (chrome antimony titanium).

Aluminum oxide, preferably in powdered form, can be used as a solar-reflective additive in a colored formulation to improve the solar reflectivity of colored roofing granules without affecting the color. The aluminum oxide should have particle size less than #40 mesh (425 micrometers), preferably between 0.1 micrometers and 5 micrometers. More preferably, the particle size is between 0.3 micrometers and 2 micrometers. The alumina should have a percentage of aluminum oxide greater than 90 percent, more preferably greater than 95 percent. Preferably the alumina is incorporated into the granule so that it is concentrated near and/or at the outer surface of the granule.

A colored, infrared-reflective pigment can also be employed in the roofing granules for use herein. Preferably, the colored, infrared-reflective pigment comprises a solid solution including iron oxide, such as disclosed in U.S. Pat. No. 6,174,360, incorporated herein by reference. The colored infrared-reflective pigment can also comprise a near infrared-reflecting composite pigment such as disclosed in U.S. Pat. No. 6,521,038, incorporated herein by reference. Composite pigments are composed of a near-infrared non-absorbing colorant of a chromatic or black color and a white pigment coated with the near-infrared non-absorbing colorant. Near-infrared non-absorbing colorants that can be used include organic pigments such as organic pigments including azo, anthraquinone, phthalocyanine, perinone/perylene, indigo/thioindigo, dioxazine, quinacridone, isoindolinone, isoindoline, diketopyrrolopyrrole, azomethine, and azomethine-azo functional groups. Preferred black organic pigments include organic pigments having azo, azomethine, and perylene functional groups. When organic colorants are employed, a low temperature cure process is preferred to avoid thermal degradation of the organic colorants. Accordingly, in such embodiments the top coat can be formed after the base particle is fired.

Algaecidal species (e.g., such as inorganic salts and oxides) can be provided as part of the material used to coat a base particle when providing a coated algaecidal granule. In the case of granules having algaecidal. Other techniques, such as impregnation from aqueous solution into pores of a granule, can also be used.

Another aspect of the present disclosure provides for an algae-resistant roofing shingle comprising a shingle substrate; and adhered to the top surface of the shingle substrate, the roofing granule mixture according to the present disclosure as described herein.

Another aspect of the present disclosure provides a method for producing an algae-resistant roofing shingle comprising providing a shingle substrate; and adhering to a top surface of the shingle substrate, the roofing granule mixture as described herein.

In certain embodiments of the present disclosure, the roofing granule mixture according to the present disclosure as described herein are adhered on at least a portion of the top surface of the shingle substrate. In certain embodiments, the roofing granules mixture evenly dispersed over the top surface of the shingle substrate.

In certain embodiments as otherwise described herein, the shingle substrate comprises a bituminous material, the shingle substrate includes a base sheet having a top surface and a bottom surface, having a bituminous material disposed thereon. As the person of ordinary skill in the art will appreciate, the bituminous material can be coated on both surfaces of, or even saturate, the base sheet. A variety of materials can be used as the base sheet, for example, conventional bituminous shingle or membrane substrates such as roofing felt or fiberglass. The bituminous material also has a top surface. A roofing granule mixture as described herein is adhered on the top surface of the shingle substrate (e.g., the top surface of the bituminous material), such that the roofing granules substantially coat the bituminous material in a region thereof. The region can be, for example, the exposure zone of a roofing shingle, or a region that is otherwise to be exposed when the roofing product is installed on a roof. The roofing granule mixture are desirably embedded somewhat in the bituminous material to provide for a high degree of adhesion. As the person of ordinary skill in the art will appreciate, other granular or particulate material can coat the bituminous material in regions that will not be exposed, e.g., on a bottom surface of the roofing shingle, or in a headlap zone of a top surface of the roofing shingle, as is conventional.

EXAMPLES

The Examples that follow are illustrative of specific embodiments of the process of the disclosure, and various uses thereof. They are set forth for explanatory purposes only, and are not to be taken as limiting the scope of the disclosure.

Example 1. Conventional Algae-Resistant Granules vs. Second Class of Roofing Granules

The present inventors have found that by using a roofing granule mixture comprising a first class of roofing granules consisting of non-algae-resistant roofing granules, a second class of roofing granules consisting of algae-resistant roofing granule having a particle size of at most 0.9 mm, the surface area of the algae-resistant roofing shingle covered by algae-resistant granules is increased when compared to using conventionally sized algae-resistant granules applied at the same weight percent. FIG. 2 shows a picture of a part of a roofing shingle covered with a mixture of roofing granules comprising 10% of conventional algae-resistant roofing granules and FIG. 3 . shows a picture of a part of a roofing shingle covered with a mixture of roofing granules comprising 10% of the second class of roofing granules consisting of algae-resistant roofing granules. In both cases, the algae-resistant roofing granules comprise copper. In both of FIG. 2 and FIG. 3 , the darker sports correspond to the algae-resistant roofing granules. From the pictures of FIG. 2 and FIG. 3 , it is clear that the number of dark spots is greater in FIG. 3 , with the second-class of roofing granules, than in FIG. 2 , with the conventional algae-resistant granules. Here, the present inventors have found that using the second class of roofing granules consisting of algae-resistant granules with a particles size of at most 0.9 mm increases the spot coverage and surface area covered on a roofing shingle by algae-resistant granules.

For example, current algae-resistant roofing shingles have a size distribution from about 0.425 mm to about 0.17 mm, with greater than 70% of the sizes ranging from 0.85-1.77 mm, as shown in FIG. 1 . By using a second class of roofing granules that have an average size that is roughly half of the conventional roofing granules, the surface area of a shingle covered by the second class of roofing granules will be roughly twice that of a shingle covered with conventional algae-resistant granules. Other differences in using the second class of roofing granules versus conventional algae-resistant roofing granules to make a roofing shingle are shown in Table 1.

TABLE 1 Total Algae- Rough Volume Surface Total covered resistant average per area per Total Total granule shingle granule granule average average granules granules surface surface weight % size granule granule amount volume area spots Second 1× ~1/2 ~1/8 ~1/4 ~8× 1× ~2× ~2× class or roofing granule shingle (vs conventional shingle)

Example 2. Algae Chamber Testing

Conventional roofing material coupons were made by coating a mixture of 90 wt % colored granules and 10 wt % conventional copper-based algae-resistant granules on to sections of bituminous shingle material. Test roofing material coupons were made in similar fashion, but using finer-sized copper-based algae-resistant granules. The conventional algae-resistant granules were as described above and the fine-size algae-resistant granules were much smaller; this was the only difference between the samples. The samples were subjected to identical algae testing.

As shown in the pictures of FIG. 4 , there was less algae growth on the test samples than on the conventional samples. Without intending to be bound by theory, the present inventos surmize that the surface coverage of the fine-size algae-resistant granules is significantly greater, e.g., about a 71% increase, than for the conventional algae-resistant granules. The present inventors suggest that distribution the finer-sized algae-resistant granules over a greater amount of the surface results in a greater effect on reduction of algae growth compared to larger size granules—even though an equivalent amount of copper granules (by weight) were used.

Various aspects and embodiments of the disclosure are provided by the following enumerated embodiments, which may be combined in any number and in any combination that is not technically or logically inconsistent.

Embodiment 1. A roofing granule mixture, the mixture consisting of:

-   -   a first class of roofing granules consisting of         non-algae-resistant roofing granules; and     -   a second class of roofing granules consisting of algae-resistant         roofing granules having a d50 particle size of at most 0.9 mm.

Embodiment 2. The roofing granule mixture of embodiment 1, wherein the first class of roofing granules has a d50 particle size in the range of 0.7 mm to 5 mm (e.g., in the range of 0.7-3 mm, or 0.7-2 mm).

Embodiment 3. The roofing granule mixture of embodiment 1, wherein the first class of roofing granules has a d50 particle size in the range of 1 mm to 5 mm (e.g., in the range of 1-3 mm, or 1-2 mm).

Embodiment 4. The roofing granule mixture of embodiment 1, wherein the first class of roofing granules has a d50 particle size in the range of 1.5 mm to 5 mm (e.g., in the range of 1.5-3 mm, or 1.5-2.5 mm).

Embodiment 5. The roofing granule mixture of any of embodiments 1-4, wherein the first class of roofing granules is present in an amount in the range of 70-99 wt % of the total mixture, e.g., in an amount in the range of 70-95 wt %, or 70-90 wt %, or 70-85 wt %, or 70-80 wt %, or 75-95 wt %, or 75-90 wt %, or 75-85 wt % of the total mixture.

Embodiment 6. The roofing granule mixture of any of embodiments 1-4, wherein the first class of roofing granules are present in an amount in the range of 80-99 wt % of the total mixture, e.g., in an amount in the range of 80-95 wt %, or 80-90 wt %, or 85-95 wt % of the total mixture.

Embodiment 7. The roofing granule mixture of any of embodiments 1-6, wherein the second class of roofing granules has a d50 particle size of at most 0.8 mm (e.g. at most 0.7 mm).

Embodiment 8. The roofing granule mixture of any of embodiments 1-7, wherein the second class of roofing granules has a d50 particle size of at most 0.6 mm (e.g. at most 0.5 mm).

Embodiment 9. The roofing granule mixture of any of embodiments 1-8, wherein the second class of roofing granules has a d10 particle size of at least 0.1 mm, e.g., at least 0.2 mm.

Embodiment 10. The roofing granule mixture of any of embodiments 1-9, wherein the second class of roofing granules has a d90 particle size of at most 1.5 mm, e.g., at most 1.0 mm, or at most 0.8 mm.

Embodiment 11. The roofing granule mixture of any of embodiments 1-10, wherein the second class of roofing granules has a d50 particle size that is no more than 70%, e.g., no more than 60%, of the d50 particle size of the first class of roofing granules.

Embodiment 12. The roofing granule mixture of any of embodiments 1-10, wherein the second class of roofing granules has a d50 particle size that is no more than 50%, e.g., no more than 40%, of the d50 particle size of the first class of roofing granules.

Embodiment 13. The roofing granule mixture of any of embodiments 1-12, wherein the second class of roofing granules are present in an amount in the range of 1-30 wt % of the total mixture, e.g., in an amount in the range of 1-25 wt %, or 1-20 wt %, or 1-15 wt %, or 1-10 wt %, or 3-30 wt %, or 3-25 wt %, or 3-20 wt %, or 3-15 wt %, or 3-10 wt %, or 5-30 wt %, or 5-25 wt %, or 5-20 wt %, or 5-15 wt % of the total mixture.

Embodiment 14. The roofing granule mixture of any of embodiments 1-12, wherein the second class of roofing granules are present in an amount in the range of 10-30 wt % of the total mixture, e.g., in an amount in the range of 10-25 wt %, or 10-20 wt %, or 15-30 wt %, or 15-25 wt %, or 20-30 wt % of the total mixture.

Embodiment 15. The roofing granule mixture of any of embodiments 1-14, wherein the second class of roofing granules comprises an organic algaecide, an inorganic algaecide, or combinations thereof.

Embodiment 16. The roofing granule mixture of any of embodiments 1-14, wherein each of the second class of roofing granules comprise an organic algaecide.

Embodiment 17. The roofing granule mixture of embodiment 16, wherein the organic algaecide is independently selected from zinc pyrithione or 4,5-dichloro-2-n-octyl-4-isothiazoline-3-one (DCOIT).

Embodiment 18. The roofing granule mixture of any of embodiments 1-14, wherein each of the second class of roofing granules comprise an inorganic algaecide.

Embodiment 19. The roofing granule mixture of embodiment 18, wherein the inorganic algaecide of the second class of roofing granules is selected from the group consisting of copper species (e.g., copper oxide), zinc species (e.g., zinc oxide), silver species and anatase titanium oxide.

Embodiment 20. The roofing granule mixture of embodiment 18, wherein the inorganic algaecide of the second class of roofing granules is selected from the group consisting of copper species (e.g., copper oxide), and zinc species (e.g., zinc oxide).

Embodiment 21. The roofing granule mixture of embodiment 18, wherein the inorganic algaecide of the second class of roofing granules is a copper species (e.g., copper oxide).

Embodiment 22. The roofing granule mixture of any of embodiments 15-21, wherein the algaecide is present in the second class of roofing granules in the range of 1 wt % to 50 wt %, e.g., 5 wt % to 50 wt %, or 10 wt % to 50 wt %, or 15 wt % to 50 wt % of the granule mass.

Embodiment 23. The roofing granule mixture of any of embodiments 15-21, wherein the algaecide is present in the second class of roofing granule in the range of 1 wt % to 25 wt %, e.g., 5 wt % to 25 wt %, or 10 wt % to 25 wt % of the granule mass.

Embodiment 24. The roofing granule mixture of any of embodiments 15-21, wherein the algaecide is present in the second class of roofing granule in the range of 1 wt % to 15 wt %, e.g., 5 wt % to 15 wt %, or 1 wt % to 10 wt % of the granule mass.

Embodiment 25. A method of producing a mixture of roofing granules accordingly to any of embodiments 1-24 comprising:

-   -   providing a plurality of base particles;     -   splitting the plurality of base particles into a first batch and         a second batch,         -   wherein the second batch of base particles have a d50             particle size of at most 0.9 mm;     -   applying a first top coat to the first batch to form a first         class of roofing granules, wherein the first top coat comprises         at least one colorant;     -   applying a second top coat to the second batch to form a second         class of roofing granules, wherein the second top coat comprises         at least one algaecide and at least one colorant; and     -   blending the first class of roofing granules and the second         class of roofing granules,         -   wherein the second class of roofing granules are present in             an amount in the range of 1-30 wt % of the total mixture.

Embodiment 26. The method of embodiment 25, wherein the second batch has a d50 particle size that is no more than 70%, e.g., no more than 60%, of the d50 particle size of the first batch.

Embodiment 27. The method of embodiment 25, wherein the second batch has a d50 particle size that is no more than 50%, e.g., no more than 40%, of the d50 particle size of the first batch.

Embodiment 28. The method of any of embodiments 25-28, wherein the splitting is performed by sieving, with base particles retained by a sieve being in the first batch, and base particles passing through the sieve being in the second batch.

Embodiment 29. An algae-resistant roofing shingle comprising:

-   -   a shingle substrate; and     -   adhered to a top surface of the shingle substrate, the roofing         granule mixture according to any of embodiments 1-28.

Embodiment 30. A method for producing an algae-resistant roofing shingle comprising:

-   -   providing a shingle substrate; and     -   adhering to a top surface of the shingle substrate the roofing         granule mixture according to any of embodiments 1-28.

It will be apparent to those skilled in the art that various modifications and variations can be made to the processes and devices described here without departing from the scope of the disclosure. Thus, it is intended that the present disclosure cover such modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.

Additional aspects of the disclosure are provided by the following claims, which can be combined and permuted in any number and in any combination that is not technically or logically inconsistent. 

We claim:
 1. A roofing granule mixture, the mixture consisting of: a first class of roofing granules consisting of non-algae-resistant roofing granules; and a second class of roofing granules consisting of algae-resistant roofing granules having a d50 particle size of at most 0.9 mm.
 2. The roofing granule mixture of claim 1, wherein the first class of roofing granules has a d50 particle size in the range of 1 mm to 5 mm.
 3. The roofing granule mixture of claim 1, wherein the first class of roofing granules has a d50 particle size in the range of 1.5 mm to 5 mm.
 4. The roofing granule mixture of claim 1, wherein the first class of roofing granules is present in an amount in the range of 70-99 wt % of the total mixture\.
 5. The roofing granule mixture of claim 1, wherein the second class of roofing granules has a d50 particle size of at most 0.8 mm.
 6. The roofing granule mixture of claim 1, wherein the second class of roofing granules has a d50 particle size of at most 0.5 mm.
 7. The roofing granule mixture of claim 1, wherein the second class of roofing granules has a d10 particle size of at least 0.1 mm.
 8. The roofing granule mixture of claim 1, wherein the second class of roofing granules has a d90 particle size of at most 1.0 mm.
 9. The roofing granule mixture of claim 1, wherein the second class of roofing granules has a d50 particle size that is no more than 60% of the d50 particle size of the first class of roofing granules.
 10. The roofing granule mixture of claim 1, wherein the second class of roofing granules has a d50 particle size that is no more than 40% of the d50 particle size of the first class of roofing granules.
 11. The roofing granule mixture of claim 1, wherein the second class of roofing granules are present in an amount in the range of 1-30 wt % of the total mixture.
 12. The roofing granule mixture of claim 1, wherein the second class of roofing granules comprises an organic algaecide, an inorganic algaecide, or combinations thereof.
 13. The roofing granule mixture of claim 1, wherein each of the second class of roofing granules comprise an organic algaecide.
 14. The roofing granule mixture of claim 1, wherein each of the second class of roofing granules comprise an inorganic algaecide, wherein the inorganic algaecide of the second class of roofing granules is selected from the group consisting of copper species, zinc species, silver species and anatase titanium oxide.
 15. The roofing granule mixture of claim 14, wherein the inorganic algaecide of the second class of roofing granules is a copper species.
 16. The roofing granule mixture of claim 14, wherein the algaecide is present in the second class of roofing granule in the range of 1 wt % to 15 wt % of the granule mass.
 17. A method of producing a mixture of roofing granules accordingly to claim 1 comprising: providing a plurality of base particles; splitting the plurality of base particles into a first batch and a second batch, wherein the second batch of base particles have a d50 particle size of at most 0.9 mm; applying a first top coat to the first batch to form a first class of roofing granules, wherein the first top coat comprises at least one colorant; applying a second top coat to the second batch to form a second class of roofing granules, wherein the second top coat comprises at least one algaecide and at least one colorant; and blending the first class of roofing granules and the second class of roofing granules, wherein the second class of roofing granules are present in an amount in the range of 1-30 wt % of the total mixture.
 18. The method of claim 17, wherein the splitting is performed by sieving, with base particles retained by a sieve being in the first batch, and base particles passing through the sieve being in the second batch.
 19. An algae-resistant roofing shingle comprising: a shingle substrate; and adhered to a top surface of the shingle substrate, the roofing granule mixture according to claim
 1. 20. A method for producing an algae-resistant roofing shingle comprising: providing a shingle substrate; and adhering to a top surface of the shingle substrate the roofing granule mixture according to claim
 1. 